Metallic toner fluid compositions are known in the toner fluid art. U.S. Pat. Nos. 5,089,362, 4,985,321 and 4,892,798 disclose metallic toner fluid compositions and their use in making metallic coatings. The metallic toner fluid compositions contain colloidal, elemental metal particles dispersed in nonpolar organic carrier liquids. Surfactants are employed in the nonpolar carrier liquids to charge and stabilize the colloidal metal dispersions. These patents disclose that the metallic toner fluid compositions can be prepared using a gas evaporation reactor (GER), a Klabunde-style static reactor, or a Torrovap.TM. rotary reactor (Torrovap Industries, Markam, Ontario, Canada). The GER is disclosed as being the preferred reactor for making colloidal metal dispersions. Although these reactors may be suitable for making colloidal metal dispersions, each of these reactors, including the preferred GER, provide difficult and mechanically-complicated ways of generating metallic particles for toner fluids.
For example, the GER generates metal particles from bulk metal under very stringent operating conditions. The metal is heated in a furnace chamber to a temperature that can be in excess of 1000.degree. C. under a relatively low vacuum. The metal particles that form from this heating are carried from the furnace chamber to the carrier liquid by an inert gas. Frequently, vacuum leaks occur in the GER, causing an increase in particle size an oxidation of the metal particles (when oxidizable metals are used). In addition, it is very difficult, if not impossible, to generate small metal particles at a fast rate; thereby making a commercialized process impractical. Large metal particles are not as suitable for use in a metallic toner fluid composition because the dispersions tend to be less stable, and when the large particles are deposited on a substrate they provide low image resolutions. High resolutions are needed to make good graphic images.
U.S. Pat. No. 4,252,677 discloses a method of preparing a dispersion of colloidal nickel, palladium, or platinum metal particles in the size range of about 10 to 200 Angstroms. The method comprises preparing a solution of a functional polymer in an inert solvent, and incrementally adding thereto an organometallic metal precursor containing nickel, palladium, or platinum. The temperature of the solution is sufficiently high to decompose the organometallic metal precursor to yield colloidal metal particles. The only palladium and platinum organometallic metal precursors that are disclosed in this patent are dichloroplatinumdicarbonyl and dipalladiumchlorodicarbonyl. These organometallic metal precursors have the carbon atom bound directly to the metal atom and contain neutral carbonyl functionality, and therefore require an anionic species, in this case, chloride, to balance the positive charge of the metal. Chloride, however, as a negatively-charged species, may have a deleterious effect on the stability of the dispersion, and hence its use as a toner fluid. Further, the organometallic palladium and platinum salts disclosed in U.S. Pat. No. 4,252,677 are not commercially available and are very difficult to prepare. For example, the preparation of the dipalladiumchlorodicarbonyl starting material calls for the use of perezone, a quinone-type natural product extracted from certain varieties of the Perezia root. See Garcia et al., Structure of Di-.mu.-chlorobis(dicarbonylpalladium), C43 Acta, Cryst. 1679-81 (1987); Gonzalez et al., The Electrochemical Reduction of Perezone in the Presence of Benzoic Acid in Acetonitrile, 310 J. Electronic Chem. 293-303 (1991); and Garcia et al., Perezone and Related Sesquiterpenes from Parvifoline, 50 J. Nat. Prods, 1055-1058 (November-December 1987).